In recent years, semiconductor integrated circuits are increasingly made more miniscule, and a mechanism for stabilizing an internal operation and a control mechanism for unleashing the full power of the real circuit are demanded in designing semiconductor integrated circuits. To ensure a high-speed operation of a semiconductor integrated circuit, the internal operation frequency is increased to perform an inspection at the shipment of the semiconductor integrated circuit. Further, to assure its operation as a product, an upper limit of the operation frequency of the semiconductor integrated circuit is decided with an operation frequency at which the circuit can operate under the worst conditions, at the shipment of the semiconductor integrated circuit. (Refer to Japanese Published Patent Application No. Hei. 05-264667.)
The conventional operation verification system, however, has following problems.
Since the operation frequency needs to be increased to perform verification of a high-speed operation, it can be supposed to mount a high-performance tester that can input a high-speed clock for the verification. However, it is difficult in practice to mount such a tester to verify a high-speed operation from the point of view of circuit scale or costs.
Further, as for stable operation assurance such as that at the high-speed operation, that with respect to supply voltage and that with respect to peripheral temperature, verification is needed assuming all possible conditions in the verification at the shipment of semiconductor integrated circuits, because the stable operation verification is not performed at the mounting of the real device. Consequently, even when the mounted semiconductor integrated circuit has enough arithmetic ability, only a minimum level of assurance is obtained. In addition, as the stable operation assurance cannot be verified at the mounting, there is no criteria for making judgements for relaxation of a frequency control accuracy, reduction of the power voltage, relaxation of a temperature control setting target and a temperature control accuracy and the like, within ranges in which the internal operation circuit stably works. Accordingly, respective control circuits operate at capabilities that are higher than their optimal minimum capabilities.